1. Field of the Invention
The present invention relates to a high frequency glass antenna for automobiles, particularly to a high frequency glass antenna for automobiles used for transmitting/receiving an electric wave of a band more than UHF band (300 MHz or more).
2. Related Art
As a high frequency glass antenna for automobiles used for transmitting/receiving an electric wave of a high frequency band such as 300 MHz or more, there have been provided high frequency glass antennas suitable for an automobile communication means utilizing a GPS space satellite signal (1.575.42 MHz), a TV broadcasting wave (471-771 MHz), 800 MHz band (810-960 MHz), or 1.5 GHz band (1.429˜1.501 GHz) for automobile telephones, for example.
In these high frequency glass antennas for automobiles, a directivity is required, because if a glass antenna receives electric waves coming from various directions, then a ghost is generated due to the phase difference among the received waves.
When such a glass antenna is provided on a front window or rear window of an automobile, the antenna is to be provided at the region near to the metal portion of a body, because a view field of a driver must be maintained for the front window and heating lines are formed on the rear window.
Japanese Patent Publication number 2002-135025 discloses the receiving system utilizing a YAGI antenna (comprising a director and reflector) showing a strong directivity for one direction as a glass antenna having less effect to a multi-path when a running automobile receives an electric wave.
The high frequency glass antenna for automobiles disclosed in above-described Japanese Patent Publication utilizes the metal portion of a body as a reflector, so that the directivity of the glass antenna is decided by the position of the metal portion. This causes a problem such that the freedom of a design for a directivity is disturbed. For example, in the case that an antenna element is positioned horizontally near to the roof of a body on an inclined front window or rear window, the antenna has a directivity in an inclined direction of the window, i.e., a downward direction. This means that the antenna has no effective directivity in a horizontal direction or elevation direction which is the direction of a coming broadcasting wave.